Pharmacolite
(repeating unit)CaHAsO4·2(H2O) IMA symbol Pmc[1] Strunz classification 8.CJ.50 Dana classification 39.1.1.2 Crystal system Monoclinic Crystal class Domatic (m)
(same H-M symbol) Space group Ia Unit cell a = 5.959 Å,
b = 15.313 Å,
c = 6.357 Å;
β = 114.67°; Z = 4 Identification Color Colorless, white, pale gray Crystal habit Commonly acicular, silky fibrous, botryoidal to stalactitic; rare as elongated flattened crystals Cleavage Perfect on {010} Fracture Uneven Tenacity Flexible Mohs scale hardness 2 – 2.5 Luster Vitreous, pearly on cleavages Diaphaneity Transparent to translucent Specific gravity 2.53 – 2.725 Optical properties Biaxial (−) Refractive index nα = 1.580 – 1.583 nβ = 1.589 – 1.590 nγ = 1.590 – 1.594 Birefringence δ = 0.010 – 0.011 Pleochroism Not pleochroic 2V angle Measured: 77° References [2][3][4]
(same H-M symbol)
b = 15.313 Å,
c = 6.357 Å;
β = 114.67°; Z = 4
Pharmacolite is an uncommon calcium arsenate mineral with formula CaHAsO4·2(H2O). It occurs as soft, white clusters of fibrous crystals and encrustations which crystallize in the monoclinic system. It is the arsenate analogue of the sulfate gypsum and the phosphate brushite.
Discovery and occurrence
Pharmacolite was first described in 1800 for an occurrence in the Sophia Mine in the Böckelsbach Valley of Wittichen, Schenkenzell, Black Forest, Baden-Württemberg, Germany. The name is from the Greek φάρμακον ("pharmakon"), alluding to its poisonous arsenic content.[2]
It forms by secondary (oxidizing) processes from primary arsenic minerals. It is associated with picropharmacolite, hornesite, haidingerite and rosslerite.[2][3]